NO148093B - GYROM ENGINE DRIVE DEVICE FOR GYRO PLATFORM. - Google Patents

Description

The invention relates to a gyromotor drive device for gyro platforms comprising at least one vertical gyroscope motor and one azimuth gyroscope motor, both of which are polyphase motors normally operating at a first frequency, and which are fed from a supply unit comprising a plurality of electronic switches to to convert a direct voltage into an alternating voltage with a rectangular waveform, as well as comprising a device for generating waveform control signals with the motor's normal operating frequency for controlling the electronic switches.

In the case of gyro-stabilized platforms for inertial control, it is common practice to start the engines at low temperatures (0°C) during a very short period of time (2 seconds). This is necessary due to the need for rapid response of gyrocompasses within minutes in combat aircraft.

Another requirement for such equipment is that the motors' bearings must have a long service life. This has made it necessary to use lubricating oil with a relatively high viscosity for the bearings, which in turn makes the problem of cold starting particularly serious, since such oils become even more viscous at low temperatures.

The traditional solution according to the prior art is to program the power supply during the starting time to deliver a high voltage to bring the motors up to saturation and to maximum torque. This means that the power supply system must be designed for a maximum total power during the start-up period that is much greater than the power during normal operation. In a similar way, the switching unit to convert direct current into alternating current for operation of the motor must also be dimensioned for the higher voltage.

Although the existing solution is thus usable, it is only achieved at the expense of increased material requirements and increased weight of the apparatus. Thus, there is a need for a gyromotor drive device which keeps the needs for power supply and switching components to a minimum, more specifically to what is needed for normal operation, but still provides a quick start at low temperatures.

In the case of a device as indicated at the outset, the fact that gyromotors are normally of the hysteresis synchronous motor type is used. In the case of a balanced, multiphase hysteresis motor, the starting torque is mainly independent of the frequency and dependent on the magnetizing current up to saturation. During normal use, the engine is operated at a considerable distance from the saturation state, in order to provide satisfactory power without excessive heating. The real starting torque is therefore considerably less than the maximum that the iron in the motor can produce. As the gyro's magnetizing current frequency must be very accurate, it is common to establish the gyro wheel frequency by counting down from a crystal clock. As soon as the required frequency is achieved, it is used to control a switching unit that converts the direct current energy into alternating current energy to operate the gyroscope's motor.

One can make use of these conditions to obtain an improved drive device that does not require higher starting voltages than the normal ones, thus making it possible to use a weaker dimensioned power supply system and an inverter unit dimensioned for lower voltages. You thus get a frequency lower than normal by expanding the logical countdown system.

If e.g. the normal frequency was 480 Hz., could

it is divided further to give a frequency of 240 Hz. As the motor impedance is essentially inductive, it will draw approximately double the current at the same voltage. Thereby, the engine's torque is essentially doubled. Of course, the increase in current and torque will depend on the special design of the motor in question. E.g. it will depend on how close to saturation the motor normally works, the motor's direct current resistance, the special limitations of the direct current supply system, etc.

According to the present invention, one introduces

in this connection, a sequence program, so that power is delivered in turn to the different phases of more than one motor. More specifically, a gyromotor drive device is of the specified type

primarily characterized by a device for, on the basis of said normal control signals, to generate a series of other control signals with a lower frequency, and a sequence control device for transmitting said control signals to the switches during the start of the motors so that the following functional sequence is obtained:

- first, current with the aforementioned lower frequency is supplied

a first phase winding on both motors,

- then the other phase windings are supplied on one of the motor-

one with the lower frequency in a fixed period of time; after which they

- is de-energized and the other windings of the second motor are supplied with the mentioned lower frequency; - and finally, after another set period of time, all windings on both motors are energized at normal frequency.

This leads to being able to deliver the maximum available power to the engine that is about to be started. E.g. must a power supply unit in a two-motor system normally supply two motors. If the sequence of power delivery during starting is adjusted so that only one motor is supplied at a time, the unit will have sufficient available power to supply this motor with twice its normal current to produce the required starting torque.

As will be explained more fully in the following detailed description, changes in frequency and/or delivery sequence can be made as needed for any particular situation. Furthermore, the present invention can be used in connection with other types of alternating current motors, such as e.g. multi-phase induction motors and synchronous motors with distinct poles. Fig. 1 shows the current-voltage characteristic for a typical power supply unit used in connection with the present invention, together with load lines for different forms of motor operation. Fig. 2 is a block diagram of the device according to the invention. Fig. 3 is a waveform diagram illustrating the waveforms used for magnetizing the motors according to the invention.

Fig. 4 is a coupling core for the gyro wheel supply unit

on fig. 2, and

fig. 5 is a logic diagram for the logic unit for the operation of the gyroscope motor in the schematic of FIG. 2.

To illustrate the present invention, the starting point is an inertial platform with at least two gyroscopes. Furthermore, for the following explanation, it will be assumed that there are two gyroscopes, namely one vertical gyroscope and one azimuth gyroscope. Furthermore, it will be assumed that the normal operating frequency for the gyroscopes is 480 Hz. Fig. 1 shows the relationship between current and voltage from the direct current supply unit, which is equipped with current limitation. The figure shows load lines for different working conditions. Thus, the load line 11 is seen for one motor at 480 Hz, a load line 13 for two motors at 480 Hz. and a load line 15 which suggests one and a half motors at 240 Hz. Under the assumption of no saturation and small ohmic winding resistance, the load line 13 also applies to one motor with 240 Hz. Fig. 2 shows a block diagram of the device according to the invention. It includes a current limiting direct current source 17, a clock 19, a countdown logic 21 and a gyrowheel supply unit 27. Two pairs of windings are connected to the output of the gyrowheel supply unit. To a pair of terminals Li and L2, first phase windings 29 and 31 are connected in parallel, connected respectively to a vertical -gyroscope and an azimuth gyroscope. Also shown are a pair of windings 33 and 35, of which winding 33 is connected across terminals L3 and L4, and winding 35 across terminal L4 and a terminal L5. Winding 33 is the vertical gyroscope's second phase winding. Winding 35 is the second phase winding of the azimuth gyroscope. The purpose of the med sequence link is to ensure that only one motor is started at a time. The sequence link is a simple timing control link which g ir a series of discrete output signals in response to input clock signals. These signals are produced in the order D-10, D-12, D-8 and D-6.

The sequence link 23 is a known device that is used in existing starting devices. The discrete signal D-10 appears as soon as power is supplied to the device. The sequence link 23 has an input (not shown) which reports that the temperature 0°C has been reached. At temperatures below 0°C, heating elements are used to heat up the device before starting. The signal D-12 occurs at a time X,

when 0°F (= -17.8°C) is reached (it could be the same time as when D-10 acts if the platform is at about 0°F). The discrete signal D-8 occurs at a time approximately corresponding to X+2 s,

and D-6 at X+4 p.

The output signals are initially at 0 volts and rise to

5 volts, where they remain as long as the device is active. The way the output signals are used will be explained in more detail below in connection with the other units.

The countdown link is a standard counter which provides a group of ■four rectangle waves designated 480 /0°, 480 /180°, 480 ,/90° and 480 /_ 210°. The relative position of these rectangular waves in time is visualized in fig. 3. These output signals are supplied to the logic unit 25 for operation of the gyro motors. This drive logic provides corresponding output signals designated ^0°, /90°, /180° and /270° to the gyrowheel supply unit 27, which couples the DC power from the DC source to the various windings discussed above. The gyro wheel supply unit connects the direct current to the motor windings in such a way that they are supplied with an alternating current square wave. The timetable in fig. 3 is suitable for windings 29, 31, 33 and 35, as these are two-phase windings. The gyro wheel supply unit is in principle a standard device, just like the countdown link. In the main, the starting device according to the invention simply needs the addition of the gyromotor drive logic 25 between the countdown link 21, the sequence link 23 and the gyro wheel supply unit 27.

The gyro wheel supply unit is shown in more detail in fig. 4.

One sees here the terminals LI and L2 to which the windings 29 and 31 are connected via a bridge connection of switches Sl to S4. As shown, switches S1 and S2 have one terminal connected to the positive busbar, and switches S3 and S4 have one terminal connected to the negative busbar respectively. earth. The respective other terminals of switches Sl and S3 are jointly connected to terminal LI. The other terminals on switches S2 and S4 are jointly connected to terminal L2. The input signal /90° is the control signal for switch Sl and switch S4, and the signal /_ 210° is the control signal for switches S2 and S3. The switches are shown schematically, but in reality will of course be semiconductor switches. It can be seen that the switches Sl and S4 will be connected together, and likewise the switches S2 and S3. From fig. 3, it will be seen that these connection conditions will lead to the imposition of an alternating current waveform over the windings 29 and 31. The windings 33 and 35 are supplied in a similar way by means of switches S5 to S10. Disregarding ports 37 to 40 for now, i.e. assuming they are open, the /180° signal will control switches S7, S6 and S10, and the /0° signal will control switches S5, S8 and S9. Thus, during the /0° part of the cycle, switches S5 and S8 will be connected and supply winding 33. Switches S8 and S9 will be connected and supply winding 35. During the next half of the cycle, / 180°, switches S6 and S7 will be connected and supply the winding 33, and S6 and S10 be connected and supply the winding 35. Again the windings will be supplied with a full alternating current square wave by means of this device. As will be explained more fully later, during normal operation the various 480 Hz signals will be connected through the gyro motor drive logic unit 9 gyro wheel supply unit to drive the two motors at 480 Hz. Because of AND gates 37 to 40, switches S5 and S7 only respond when output signal D-12 is present. Switches S9 and S10 only react when D-8 is present. A further switch Sil, shown in fig.2, is inserted between the current source and the gyro wheel supply unit, so that direct current power is only supplied to this unit when the signal D-10 is present.

Fig. 5 illustrates the gyromotor drive logic in more detail. In response to the output signals from the sequencer 23, the gyro motor drive logic supplies appropriate pulses to the gyro wheel supply unit, either at the normal frequency of 4 80 Hz during normal operation or at 240 Hz during start. The logic unit used in the circuits here is a diode transistor logic (DTL), unless otherwise stated. As shown, the four 480 Hz signals at 0°, 180°, 90° and 270° are supplied as input signals to the device. At the entrance to the unit are two D-type flip-flops 51 and 53. Each of these has a set of. outputs consisting of a ready input C, a data input D and a clock input CLK. The ^/0° signal with 4 80 Hz is applied to the input CLK of the flip-flop 51. This flip-flop has its Q output fed back as a D input. This Q output is also fed as D input to the flip-flop 53. Its clock input CLK receives the J/90° signal with 480 Hz. The ready and set inputs of both flip-flops are all linked together and via a resistor 55 connected to a positive supply voltage. With this device the 480 Hz signal is frequency divided to develop the 240 /_ 0° signal

from the Q output of flip-flop 51, the 240 /180° signal from its Q output, the 240 /90° signal from the Q output of flip-flop 53 and the 240 /2 70° signal from its Q output. The signals with 480 Hz and 240 Hz are supplied as input signals to AND ports 56 to 63. The 480 / Q° signal constitutes the one input signal to AND port 56. 240 / 0°

constitutes one input signal to the AND gate 57. Similarly, the AND gates 58 and 59 receive the 480 Hz and 240 Hz/180° signals, and the AND gates 60 and 61 the /90° signals, and the AND gates 62 and the 63 / 270° signals. The gates 56 and 57 deliver their output signals as input signals to the OR gate 65. The output signals from the AND gates 58 and 59 constitute input signals to an OR gate 66, the output signals of the AND gates 60 and 61 constitute input signals to the OR gate 67, and the output signals for the AND gates 62 and 63 constitute the input signals to the OR gate 68. The output signals from the OR gates are the signals supplied to the gyro wheel supply unit 27 in fig. 2.

Above in fig. 5, there is also shown a further logic link, controlled by the sequence link 23. As shown, the signal D-6 constitutes the input signal to an inverter 70. The output signal from this inverter constitutes, together with the signal D-8, input signals to an inverting AND gate 72, whose output signal is fed together with the signal D-12 from sequence link 23. Since DTL logic is used, the common wire will be at zero if either the output signal from gate 72

or signal D-12 is zero. The output signal from the inverter 70 is delivered to a further inverter 73, whose output signal forms an activating input signal to the gates 56, 58, 60 and 62. After the inverter 73 follows a further inverter 75, whose output signal activates the gates 57, 59, 61 and 63. The gates have a third input which is always activated by the output signal from an inverter 77, whose input is connected to ground.

During operation, the sequence link, which as mentioned is a simple timing control link and can be composed of counters, with suitably decoded output signals to give the desired sequence, first supplies the output signal D-10. This signal closes the switch Sli to provide power to the gyro wheel supply unit. At this point, the outputs D-12, D-8 and D-6 will be constantly at "0". Since the signal D-6 is a "0", the inverting amplifier 70 will have its input

on "1". This "l" signal is inverted to a "0" in the inverter.73

and back to "1" via inverter 75. As a result, gates 57, 59, 61 and 63 are opened to release the 240 Hz signals. Thus, the 240 Hz signal is initially supplied to switches S1 to S4 S8 and S6 in FIG. 4. With switch S1 closed and with the 240 Hz square waves applied to the switches, switches S1 through S4 will operate

and supplying windings 29 and 31 with alternating current square waves of 240 Hz. At this point, D-12 is still "0", and so is D-8. Although the switches S6 and S8 may work, the other switches S5, S7, S9 and S10 are thus not activated, and there will be no complete circuit through the windings 33 and 35, so these will not receive power. Shortly after the windings 29 and 31 are activated, the sequencer outputs the signal D-12. When D-12 is present, i.e. is "1", AND gates 37 and 38 are opened, and switches S5 and S7 can now both be activated. Winding 33 now receives power. In other words, the vertical gyro is now fully magnetized and can begin to gain speed.

At this point, D-8 and D6 are constantly "0". Consequently, the output of the AND gate 72 with a "1" and a "0" at the input will be at "1". This output signal is connected to D-12. Since the applied logic is DTL logic, the common point will remain at "1" only if all the input signals to it are "1". With D-12 at "1" and the output from gate 72 at "1", wire 77 at the input to the gyro wheel supply unit of FIG. 2 and also in fig. 4 remain at "1" and keep ports 37 and 38 open. The first gyro motor will now be started at reduced frequency and the total current will be limited by the 240 Hz load line and the current limiting effect of the DC source. The sequencer now supplies the output signal D-8, i.e. D-8 comes on "1". D-8 constitutes the input signal to the inverting AND gate 72 in fig. 5. Since D-6 is still at "0" and the output of the inverter 70 at "1", there will now be two "l" values at the input of gate 72, and its output signal will be "0". As a result, the AND gates 37 and 38 in fig. 4 closed. Due to the binary "1" on D-8, AND gates 39 and 40 are opened. This activates switches S9 and S10 to work together with switches S6 and S8 to supply an alternating current square wave to the winding 35. Under these conditions, the vertical gyro motor operates in single-phase operation at 240 Hz. Azimut - the motor runs with both windings energized. As in the case of the vertical motor, it comes up to starting speed with 240 Hz.

After a suitable time has passed for the azimuth motor to come up to speed, the sequencer delivers D-6 as the "l" output signal. This causes the output from the inverter 70 to become "0" and the output signal from the gate 72 again becomes "1". Moreover, the output signal from the inverter 73 will now become "1" and the output signal from the inverter 75 "0". Thus, two things happen. The ports 37 and 38 are opened again/ so that the winding 33 can be supplied. Further, ports 57, 59, 61 and 63 are closed and ports 56, 58, 60 and 62 are opened to pass the 480 Hz signals to the gyro wheel supply unit 27. Now all the switches in fig. 4 stopped and supplied with 480 Hz, and both motors will come up to speed with 480 Hz. This is the final stage of the initiation.

The above explanation concerned the start of a synchronous motor. However, as mentioned, the invention can also be used in connection with other engine types. E.g. can an induction motor, which usually has a cage-shaped rotor winding, have very little starting torque. Such a motor has a speed-torque curve which is primarily a function of the rotor impedance and the sag frequency in the rotor. As the rotor approaches synchronous speed, the frequency in the rotor approaches zero. At standstill, the rotor frequency is equal to the line frequency. By using a device according to the present invention, in particular a gyro wheel supply coupling as shown in fig. 4, at a low frequency, e.g. the timing frequency at which maximum torque occurs, it is possible to start such a motor with maximum torque. A device for this purpose would simply require supplying the windings with such a frequency determined from the motor speed-torque characteristic instead of a simple halving of the "normal operating frequency. As with the embodiment just described, the total power and the magnitude of the torque will be regulated by limiting the direct current from the power source. As the motor starts up, the rotor frequency will decrease and the torque will vary. As soon as the torque has decreased and the motor has reached speed, the frequency can be changed to bring the torque back to maximum. This mode of operation can be continued step by step until the motor reaches maximum speed. Thus, one would be able to program sequence link 23 to provide a range of frequencies suitable for bringing such a motor up to speed on the basis of a prior analysis to determine the optimum switching points. It is also possible to use feedback control with the direct current and switching unit, or use a tachometer to initiate switching.

A synchronous motor with distinct poles is also hard to start.

It has no starting torque and is normally started using an induction motor winding built into the pole construction. As the compound-wound induction rotor thus approaches synchronous speed, the rotor's distinct poles lock in synchronism. As there is no sagging, the induction winding is therefore inactive. In such a motor, if the winding of such a synchronous motor with distinct poles is supplied with a current of very low frequency, i.e. approximately direct current, using a device as shown in the drawing, it will be possible to bring the rotor into phase with the stator field. By slowly increasing the frequency, limited by the rotor's ability to develop sufficient torque to accelerate the inertial load and overcome friction and constantly stay in synchronism, the motor could be allowed to start slowly and be accelerated up to the required synchronous speed. An engine of this type could then be used e.g. for a gyroscope. Such a motor could in certain cases be more efficient once it has been started, compared to a hysteresis motor.

Thus, the present invention, viewed in its broadest view, provides a device for supplying variable frequency to alternating current gyroscope motors to change their starting characteristics and thereby bring the motor up to speed without the need for greater voltages or currents than those used in normal operation. Furthermore, the invention aims to make use of the current-limiting properties of a direct current supply source to regulate the starting current in the motors-

Claims (6)

1. Gyromotor drive device for gyro platform, comprising at least one vertical gyroscope motor and one azimuth gyroscope motor, both of which are polyphase motors normally operating at a first frequency, and which are fed from a supply unit (27) comprising a plurality of electronic switches (S1 - S10) to convert a direct voltage into an alternating voltage with a rectangular waveform, as well as comprising a device (19, 21) for generating wave-shaped control signals with the motor's normal operating frequency for controlling the electronic switches, characterized by a device ( 51, 53) for, based on said normal control signals, to generate a number of other control signals with a lower frequency, and a sequence control device (23, 25, 37 - 40) for, during the start of the motors, to transfer said control signals to the switches so that there the following sequence of functions is obtained: - first current with the mentioned lower frequency is supplied to a first phase winding (29, 31) on both motors/- then the other phase windings (33) on the one of the motors with the lower frequency in a fixed period of time; after which they are - de-energized and the other windings (35) of the second motor are supplied with the mentioned lower frequency; - and finally, after another fixed period of time, all the windings (29, 31, 33, 35) of both motors are energized at normal frequency. 2. Device as specified in claim 1, characterized by means for controlling maximum starting current and torque by using a current-limiting direct current power source as power source. 3. Device as stated in claim 1, where the device for generating the normal control signals comprises: - a crystal-controlled clock (19) and - a device (21) for dividing the clock frequency down to four first control signals, each of which has the first , normal frequency, and which have the form of rectangular waves with a duration equal to half the period and are mutually offset by 90°; characterized by- a device (51, 53) for, based on said first control signals with said first frequency, to obtain four other control signals which have the same relative phase position at the second, lower frequency; - a logic device (56-63 and 65-68) which receives said first and second control signals and is adapted to respond to an input signal to selectively supply one or the other of said sets of four control signals at its output, which is connected to the gyro-wheel supply unit; - and a. sequence-determining link (23) to deliver said input signal to cause the logic device to first deliver said control signals at said second frequency for a fixed time and then deliver the control signals at said first frequency. 4. Device as stated in claim 3, characterized in that the logic device comprises a plurality of pairs of AND gates (56 and 57 - 62 and 63), where the first gate (56, 58 etc.) in each pair gets as input signal one of the mentioned first control signals with the mentioned first frequency, and the other (57, 59 etc.) receives as input signal the corresponding second control signal with the mentioned second frequency; - a plurality of OR gates (65-68) which each receive as input signals the output signals from a pair of AND gates and at their outputs deliver the control signals to the electronic switches; and - at least one inverter (75), in that the first AND ports in each pair are connected to be activated by the inverter's input signal, while the output signal from the inverter is connected as activating input to all the other ports in the aforementioned sets. 5. Device as stated in claim 3 or A", characterized in that the sequence link (23) includes a device for delivering successive output signals (D-6, D-8, D-10, D-12), wherein a first output ( D-10) is connected to connect the power source (17) to the gyro wheel supply unit (27); a second output signal (D-12), acting next, is connected to the gyro wheel supply unit to enable said one motor to be energized; a third output (D-8) is connected to said gyro-wheel supply unit to enable said second motor to be energized/ and a fourth output (D-6) is connected to the AND gates ( 56-63) over at least one inverter. 6. Device as stated in claim 5, characterized by an inverter (70) which has as input the aforementioned fourth output (D-6) from the sequence link, and an inverting AND gate (72) which has its inputs connected to the output from the inverter and the third output signal (D-8) from the sequence link, and in that the output from the AND gate is connected to the said second output (D-12) from the sequence link, whereby occurrence of the said third output signal (D-8) will de-activate said second output (D-12), and occurrence of said fourth output signal (D-6) will activate said second output (D-12) again.